Poly[μ5-{hydrogen bis[(E)-cinnamato]}-caesium]

In the structure of the title polymeric complex, [Cs(C9H7O2)(C9H8O2)]n, a caesium salt of trans-cinnamic acid, the Cs+ ions of the two individual irregular CsO8 coordination polyhedra lie on twofold rotation axes and are linked by four bridging carboxyl O-atom donors from two cinnamate ligand species. These two ligand components are interlinked through a delocalized H atom within a short O⋯H⋯O hydrogen bond. Structure extension gives a two-dimensional coordination polymer which lies parallel to (001). The structure was determined from a crystal twinned by non-merohedry, with a twin component ratio of approximately 1:1.

The reaction of trans-cinnamic acid with caesium hydroxide in aqueous ethanol afforded crystals of the title complex, [Cs(C 9 H 7 O 2 )(C 9 H 8 O 2 )] n , (I), the structure of which is reported herein.
In the structure of (I) the asymmetric unit ( Fig. 1) comprises two independent irregular CsO 8 coordination polyhedra  Table 2). Although this phenomenon involving coordinating dimeric carboxylate species is not known among the alkali metal substituted-cinnamate structures, it is found in both ammonium hydrogen bis(3-chlorocinnamate) and ammonium hydrogen bis(3-bromocinnamate) (Chowdhury & Kariuki, 2006), with the O···H···O values [2.554 (6) Å for the 3-Cl-analogue and 2.466 (5) Å for the 3-Br-analogue] similar to that in the structure of (I). In this complex, the two Cs + ions are quadruply bridged giving a Cs1···Cs2 separation of 3.9318 (3) Å and generate an overall two-dimensional coordination polymer lying parallel to (001)

Experimental
The title compound was synthesized by heating together for 10 minutes, 148 mg (1.0 mmol) of trans-cinnamic acid and 75 mg (0.5 mmol) of CsOH in 15 ml of an 1:9 (vol/vol) ethanol-water mixture. Partial room temperature evaporation of the solution gave colourless elongated crystals of the title complex from which a specimen was cleaved for the X-ray supplementary materials analysis. These crystals were invariably twinned, a feature identified in the later structure solution and refinement routines.

Refinement
Hydrogen atoms were placed in calculated positions [C-H = 0.95 Å] and allowed to ride in the refinement, with U iso (H) = 1.2U eq (C). The carboxylic acid H-atom was found to be delocalized in a site approximating to midway between two carboxyl O-atoms of the dimeric acid-anion unit and was subsequently allowed to ride at that site, with U iso (H) = 1.5U eq (O). The presence of a non-merohedral twin was identified using TwinRotMat within PLATON (Spek, 2009) (twin law: 1 0 0, 0 1 0, 1.5 0 1) reducing the conventional R-factor from 0.23 to 0.072, with a final BASF factor (HKLF 5 format) of 0.4836. Maximum and minimum residual electron densities were 1.26 eÅ -3 (1.00 Å from Cs1) and -2.19 eÅ -3 (1.94 Å from H14B), respectively.

Figure 1
The atom-numbering scheme and the molecular configuration of the two ligands and the two CsO 8 coordination polyhedra of the title complex, with non-H atoms drawn with displacement ellipsoids at the 40% probability level. The two Cs + cations lie on twofold rotation axes. The O14A···O14B hydrogen bond with the delocalized H atom (H14B) is shown as a dashed link. [For symmetry codes: see Table 1].

Figure 2
A view of the partially expanded polymeric extension of the structure viewed along the approximate a-cell direction. Cbound H atoms are omitted. A and B denote the two different ligand components.

Figure 3
The packing of the layered structure of compound (I) viewed along b. Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq